The invention relates to a half bridge and a half bridge control method.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
A half bridge is a common circuit arrangement for providing an output to drive another device such as an AC motor or transformer. The half bridge includes switches for selectively switching the output between a positive and negative DC supply rail. By varying the duty cycle of the switches, that is to say, the on and off times within a given period, it is possible to provide the desired output levels to the AC motor.
The switches in the half bridge are semiconductor devices and it is conventional for these to be n type transistors. The switches are identified as high side and low side on the basis of their connection to the +DC or −DC supply rails. A problem with such arrangements is the need to provide boot-strapping to ensure that the high side switch gate drive is provided with a power supply when the low side switch is conducting. A typical prior art arrangement is shown in FIG. 1. The bootstrap capacitor C is monitored by a monitor circuit M. This is an analog circuit that reacts to the voltage difference across the capacitor C. When the potential difference is sufficient it allows operation of the gate driver.
A problem with this arrangement is that the monitor circuit needs to be added to every gate drive on the high side for each half bridge that may be required. A typical application of the half bridge in the field of DC motors will require two half bridges. Adding such monitor circuits to standard available half bridge components is undesirable since it adds to cost, and introduces the possibility of damage occurring due to manufacturing operations.
It would therefore be desirable and advantageous to address this problem and to provide an improved method and apparatus to obviate other prior art shortcomings and to enable a high-side (or low-side) signal based on the condition of the low-side (or high-side) signal to control the operation of a half-bridge network.